Method of treating pistons



Sept. 13, 1932. c. s. c. READ THOD OF TREATING PISTONS Filed Jan. 12,1931 jzaerzza 0 7 226 076.2%(7

Patented Sept. 13, 1932' UNITED STAT];

s PATENT. OFFICE CHARLES S. C. READ, OF TORONTO, ONTARIO, CANADA,ASSIGNOR OI GEORGE E. MATTHEWS, OF TORONTO, ONTARIO, CANADA MErHon orTREATING .rrsrons Application filed J'anuarym, 1931. Serial 1T0.508,177, aiid in Canada May 13, 1931.

Prior to this invention it has been found difficult to providesuflicient lubrication on the cylinder walls to prevent excessive wearon the piston and walls which results in 5 undesirable piston slapFurthermore when an engine becomes worn it has heretofore been necessaryto replace the old worn pistons by a new set, which involves the work ofgrinding-in the cylinders to fit the new pistons which is expensive andit has also been necessary in replacing pistons to use oversize pistons,that is, pistons somewhat larger than the original pistons in order tocompensate for the wear on the cylinder walls.

Objects of this invention are to provide a method of treatin pistonswhereby only portions of the sur ace contact with the cyl inder wall,resulting in low friction and j the diameter whereby they may be usedagain and fit tightly within the cylinder, although both cylinder andpiston are worn to a considerable extent; and also to provide a methodof making oversize pistons for use in worn engineblocks.

Other methods have been used in an at tempt to overcome thisobjectionable wear.

Pistons have been expanded, that is, the diameter of the piston has beenincreased by spreading portions of the skirt of the piston. This resultsgenerally in an elliptical or oval shaped piston which aggravates theobjectionable conditions instead of curing them. Another method has beento weld or shrink aband' of metal around the outside of the skirtportion toincrease the diameter somewhat. This makes a heavier piston,throwing the engine out of balance, the attachment ofthe band is ofteninsecure, causing damage to the cylinder walls, and the grain structureis further changed undesirably by the heating effect. In the practice ofthe method of this invention the weight of each piston remains the sameand, since no heating is necessary, the desired properties in the metalremain the same.

The article of this invention comprises a piston in which the surface orportions of good lubrication for the piston; to provide a method oftreating worn pistons to increase ting thepiston wall as by extrusion,preferv ably at the skirt portion, whereby the diameter of the piston incertain portions is increased. The invention also comprises a own-ms momethod of treating the surface of pistons to provide grooves or recessesand ridges or protuberances, which results in a better lubricated pistonas well as in enlarging the diameter of worn pistons.

In the drawing: Fig. 1 is an elevational view .of a showing theinvention; and

Fig. 2 is a perspective view of a developed section of the skirt portionof the piston.

piston The piston l is provided with-the usual head portion 2 and skirtportion 3, the head portion having the usual series of circumferentialgrooves 4 for receiving piston rings.

Adjacent the lower edge of the skirt portion of the piston of the,preferred construction is provided a circumferential band or hands ofknurling J which may be applied in any desired manner as for example bymounting the piston in a lathe and rotating it while a knurling tool isacting upon the surface. This results in a series of spaced ridges orprotuberances 6 and corresponding interipnnected grooves-7 as shown mostclearly in In the particular embodiment. disclosed, the knurling extendsfrom the lower edge of the skirt portion up to a point where the sidesof the piston are cutaway for the wrist pin bearing,ias in Fig. 1,forming two bands of knurling one on either side of the oil groove 9.However, the particular width of the' band or bandsmay be varied asdesired, as, for example, by extending the knurling only over the areabetween the oil groove andthe base of'the skirt portion. If desired, aband of knurling may also be applied adjacent the top of the pistonbetween one or more pairs of adjacent ring grooves in order to produce atighter fit at the top of the piston. It has been found, as a result ofthe knurling, that the diameter of the piston may be increased tocompensatefor wear as much as 25/1000 of an inch Without additional orremoval of any material. After the knurling operation the outer surfacemay be treated, to provide a surface of contacting areas which define aperfect cylinder and to obtain the desired piston diameter, as by agrinding or turning operation. Other treatments of the piston wall willproduce asurface having desirable characteristics similar to the knurledsurface, as for example, a series of prickpunch marks, a series ofrolled threads, or any similar extrusion of'metal on the sur face. Thesurface area of the protuberances and the amount by which the diameterof the piston is increased may be varied within wide limits, dependingon the type of treatment and the extent of such treatment. The ratio ofthe area of the protuberances which contact with the cylinder to thecorresponding area of the usual piston may be varied wide-- ly (e. g.between 25% and 75%) and is dependent on the width and depth of theindentations in the extrusion means. i

This invention also includes an embodiment in which the knurling orextruding operation is not carried entirelyaround the circumference butis confined to certain portions thereof, preferably in at least threespaced portions. In this embodiment the desired tight fit of the pistonto prevent piston-slap is obtained, due to contact with the cylinder inat least three locations around the circumference.

The surface of the piston after being treated will normally becharacterized by having a portion of the peripheral surface divided intoareas of small dimensions, certain of'the areas being located at oneradius and other areas at other radii, forming, in the preferredembodiment, a surface of small bearing areas at one radius and a seriesof interconnecting channels between said'areas at a shorter radius alongwhich channels oil may flow to lub-' ricate the bearing areas. Theseareas may have any desired surface contour; they preferably conform withthe curvature of the cylinder wall, although the surface of the 1 areasmay be rounded, providing less surface contact but allowing for moreefiicient lubrication since, by reason of the resultant spacing of theedge of the areas from the cylinder wall, the oil may readily flow ontothe areas to lubricatethe surfaces. The bearing areas or'prot-uberancesare staggered axially in the preferred embodiment, that is, the areasare not in line longitudinally of the piston. As a result of thestaggered surfaces the channels therebetween do not run direct- 1ylongitudinally of the piston permitting no direct line of flowfor 'oilpast the contactprotuberances ing surfaces of the skirt portion of thepiston and cylinder wall.

By the use of this structure on a piston, the friction between thepiston and cylinder is decreased to an appreciable extent, there being amuch smaller area of contact between surfaces; also there is less Wearon the cylinder wall because of the smaller surface contacting with thewall, thus the friction is reduced' and at the same time excessive oilleakage is prevented.

This construction is particularly applicable to worn pistons in order toenlarge the diameter, as will be apparent from a consideration of Fig.1, in order to make the diameter of the sklrt portion sufiiciently largeto prevent piston-slap, since by the knurling pressions. However, thisconstruction isalso useful on new pistons for use in new engines, sinceth1s structure of piston by reason of the increased oil supply decreasesthe wear on the engine block. In pistons of this type theskirt portionwill be made somewhat smaller than the normal size and increased by aknurling or other operation-to the normal diameter. A further use isfound in providing oversized pistons for use in worn engine blocks. Apiston of substantially normal diameter is treated by knurling or thelike, whereby the diameter is increased and compensates for the enlargeddiameter of the cylinder and avoids the necessity of buying newoversized pistons and grinding in the cylinder walls to fit the pistons.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall' within the scope of the appended claims.

I claim:

1. Method of increasing the diameter. of a piston, which comprisesextruding a peripheral surface thereof by knurling, thus providing aplurality of mutually crossinggrooves between spaced protuberanceshavingouter surface areas substantially defining a cylindrical surface.c, a

2. Method of increasing the diameter of a piston, which comprisesextruding a peripheral surface thereof by knurling, thus providing aplurality of mutually crossing grooves-extendin diagonally in relationto .the central axis of the piston between spaced having outer surfaceareas staggered in relation to said axis and substantially defining acylindrical surface.

a 3. Method of increasing the diameter of a piston, which comprisesextruding a peripheral surface thereof by knurling, thus providing aplurality of mutually crossing grooves between spaced protuberanceshaving 1 J outer surface areas substantially defining a cylindricalsurface, and thereafter subjecting the knurled portion to a finishingopera tion to cause said areas accurately to assume the form of smallportions of a cylindrical surface.

Signed by me at Toronto, Ontario, Canada, this 10th day of September,1931.

. CHARLES S. C. READ.

